Method of and apparatus for employing tuning forks to generate audio frequency current as alpha medium for sound



Aprll I, 1930. sc M 1,753,069

METHOD OF AND APPARATUS FOR EMPLOYING TUNING FORKS T0 GENERATE AUDIO FREQUENCY CURRENT AS A MEDIUM FOR SOUND Filed July 5, 1928 III ' V' I v NTORA WITNESSES Jifa ,Sg/z umnz Q MW v ATTORNEY Patented Apr. 1, 1930 UNITED STATES. PATENT OFFICE KAI SOHUHM, 01 PORT JEFFERSON, NEW YORK 'IE'IHOD OI APPARATUS E03 EMPLOYING TUNING FORKS TO GENERA'IE AUDIO IBEQUmi'CY CURRENT AS A FOB SOUND Application filed July 5, 1988. Serial No. 290,502.

This invention relates to new and useful improvements in sound regroducers and an umsroved method of soun reproduction.

no object of this invention is a new method of, producing musical notes amplified in volume.

Another object of this invention is a suitable form of apparatus for carrying out the said method.

Another object of this invention is a ".silent piano.

In accordance with this invention a tuning fork having a period. of vibration corresponding to that of a predetermined musical note, and forming in conjunction with an electromagnet situated between its free ends a substantially closed magnetic circuit, is caused to vibrate to vary the reluctance of said In etic circuit, whereby alternating current is generated in the coil of said electromagnet, the frequenc and amplitude of said'current being depen ent upon the period of vibration of said tuning fork and characteristic of the desired musical note. The current thus generated is connected to the input circuit of an' audio-frequencyamplifier whose output circuit includes a suitable form of telephone or loud speaker, whereby the musical note corresponding to the period of vibration of said tuning fork, but many times amplified, is reproduced in said telephone or I loud speaker.

Inv the drawings,-comprising but'a single sheet of two figures,,one suitable form of apparatus for performing the several steps of the said method in their proper sequence is diagrammatically and schematically set forth.

Figure 1 is a schematic diagrammatic rep resentation of a suitable form of apparatus for producing, translating, amplifying, and

reproducing, a particular musical note; and

Figure 2 is a schematic representation of a simple form of musical instrument or appacharacteristic of the period of vibration of ratusarranged to amplify and reproduce a plurality of different musical notes. It should of course be understood that the devices of Figures land 2 are merely illustrative and that the number of musical notes which may bereproduced from an apparatus constructed in accordance with and embodying the rinciple .of this invention is only limited y the number of musical notes which are audible to the human ear. One commercial form of the invention would be an'electro-mechanical piano having the scale commonly used in commercial pianos.

Referring to Figure 1, the hammer 11 at the right of the figure, which is pivoted at 14, is adapted to strike the tuning fork 3 under the control of the ivoted member 13, whenever the key 12 is d pressed to actuate said member 13. It will be understoodthat after striking the tuning fork 3, the hammer 11 will return to its normal osition under the influence of gravity or un er control of a suitable retractile spring. The tuning fork 3 may be of any preferred form of magnetic substance, the tuning fork being magnetized. The base of the tuning fork is secured as at 4: to a suitable foundation 5. An electromagnet 6 is positioned between the extremities of the prongs of the tuning fork 3 and is so adjusted with respect to said prongs that the core? of the electromagnet 6'alfords sufiicient clearance with respect to the prongs of the tuning fork 3 to permit the said prongs to freely vibrate and emit the musical note said tuning fork 3. The vibratory movement of the prongs of said tuning fork 3 causes the air ps between the polar faces of the core 7 an 4 the rongs of t e tuning fork 3 to be varied w ereb the reluctance of the magnet circuit formerl by the said tuning fork and the core piece -7 isvcaused to vary, thereby generating an alternating current in the winding of the electromagnet 6. The amplitude and frequency of the current thus generated in the winding will depend upon the period of vibration of the tuning fork, which, in turn, as is well known, depends upon the period of vibration of the desired note. The

23 of the thermionic tube 20. The filament 7 21 of said tube-is connected in series with a suitable battery 25 and a rheostat 24. A suitable telephone or loud speaker is connected by means of a plug and jack to the output circuit of said amplifier, said circuit including the plate 22 of the thermionic tube 20. It thus appears that when the key 12 is depressed of the tuning fork 3 and cause said tumng fork to vibrate in accordance with its period of vibration, which will correspond to the period of vibration of a particular musical note. The tuning fork, by varying the reluctance of the magnetic circuit, including the core 7 of the electromagnet 6, will generate an alternating current in the winding of said electromagnet having a frequency and amplitude depending upon the period of vibration of the tuning fork 3. This current may be amplified through as many sta es of audiofrequency amplificationas may e desirable before being impressed upon the circuit of an electromagnetic sound-reproducing unit.

Figure 2 is a modification of the device of Figure 1 schematically illustrative of one embodiment of the invention as applied to a device for producing a plurality of different musical notes. In Figure 2 the hammers 11 and to 52 and the associated tuning forks 3 and to 62 and electromagnets 6 and 30 to 32 are shown in plan. It should be understood however, that the number of tuning forks and associated mechanism may be increased or decreased dependin upon the mm sical scale desired. The trans ormer 8 is also modified and is provided with a secondary winding 10 windings 9, 40, 4.1 and 42, each of the said primary windings being incircuit with the' winding of its associated electromagnet irrespective of the particular apparatus employed; the windings of the several electro magnets are connected to the input circu1t of one or more audio-frequency amplifiers, and a suitable tele hone or loudspeaker common to the device orms a part of the output circuit of the amplifier system.

It thusappears that whenever one of the hammers strikes one of the tuning forks the telephone receiver or loud speaker will cause a musical note corresponding to the musical the hammer 11 will strike the prong and. with a plurality of primary note peculiar to the said tuning fork but greatly increased in volume, to be emitted, and the notesthus emitted will change as frequently as the operator depresses a different key. It thus appears that the principle of the apparatus illustrated herein may be embodied in any suitable form of musical instrument, such for example, as a piano, and the equipment required in a piano embodying the principle of this invention may be housed within a much smaller housing than the strings of the ordinary commercial piano. Furthermore, when an ordinary headgear receiver is substituted for the loud speaker, a piano constructed in accordance with the principle of the present invention may be operated without causing inconvenience to other people, because the only person who would be able to 'hear the music which is produced would be the individual'listening in the telephone receiver. It therefore appears that a piano embodying the principle of this in.- vention has an advantage not by the present commercial product in that it may be transformed into a silent piano if so desired- Of course it will be understood that the magnetized tuning fork is in reality a tuned, magnetized reed, and other forms of magnetized, tuned reeds might be used instead of a magnetized tuning fork, without departing from the spirit of the invention. Similarly, the core of the electromagnet may be a permanent magnet, in which event the tuned reedmay or may not be magnetized, as preferred.

What is claimed is:

1. The method of producing a musical note which consists in vibrating a magnetized tun ing fork whose period of vibration corresponds to the period of vibration of the desired note to vary the reluctance of a magnetic circuit including said tuning fork and the core of an electromagnet thereby generating an electric current in the of said magnet, the frequency and amplitu e of said current bein dependent u n the period of vibration of t e tuning for in amplifying the current thus generated, and in applying the current thus amplifed tothe terminals of the winding of an electro-mechanical sound reproducer to reproduce the musical note emitted by the tuning fork.

2. In a musical instrument a magnetized tuning fork, an electromagnet positioned in spaced relation between the prongs of fork, means operable to vibrate said tumng fork to generate a. current in the winding of said'electrognagnet, means for the current, an electro-mechanical sound re roducer, and'a cireuitincluding the win of said reproducer and the output circuit of sad amplifier.

3. In a musical instrument a plurality of. magnetized tumng forks, a plurality of elec- Ill tromagnets, a substantially closed magneticcircuit for each tuning fork, said magnetic circuit including said tuning fork and the core of one of s 1d electromagnets, means selectively operab e to vibrate any particular tunin fork to generate a current in the winding the electromagnet associated therewith,

' means for amplifying the current thus generof June, A. D- 1928.-

' MAX SCHUMM. 

